4R100 Flow Issues
©2006 Sonnax Industries Inc.
To help understand some of the flow issues
that plague the 4R100 converter, it’s a good idea to look
first at its ancestor, the E4OD.
The E4OD brought a new variety of TCC
problems to transmission shops. Until this time most shops had
not commonly seen the clutch-crowding condition that was all
too common in the E4OD. Keep in mind that the only experience
most shops had in diagnosing lockup problems was limited to the
TCC-shudder and engine-stall problems of the early Chryslers.
Since most of these problems turned out to be related to cooler
flow, these early Chryslers didn’t help in the
advancement of diagnostic knowledge.
Limited diagnostic abilities caused many of
the initial clutch-crowding conditions to be misdiagnosed. Most
were diagnosed as engine-performance problems – off-idle
hesitations, engine stumble or lean fuel conditions. When the
problem was finally identified correctly, it still took some
time to
identify the root cause. The technicians
knew that the TCC was dragging but didn’t know why. It
seemed natural to look for the root cause of the crowding
condition on the apply side of the circuit. The hard lessons
learned from troubleshooting the GM 125C engine-stall problem
were still fresh on most technicians’ minds. This kept
them focused on trying to figure out how the TCC apply oil was
getting into the converter when it wasn’t supposed to.
Only when the TCC apply passage between the solenoid pack and
the pump was tapped did their focus change.
The TCC-apply-oil tap showed that the
pressure remained at zero any time the circuit was not charged.
The technicians shifted their focus to the release-oil circuit.
Low pump volume at low speed would not supply sufficient
converter-charge/TCC-release oil to keep the clutch from
dragging on the cover. When the low pump volume was addressed
and a sufficient supply of release oil was restored, the
problem went away. Technicians have been aware of what happens
when converter flow is restricted in a lockup converter since
the early rear-wheel-drive Chrysler days, and the E4OD
converter has driven that realization home.
Some shops had concerns about contact
between the turbine hub and cover. Early attempts to put a
bearing or thrust washer onto the front of an E4OD turbine hub
did prevent metal-to-metal contact between the hub and cover.
These also may have created flow issues that caused some clutch
failures and/or restricted lube oil to the transmission and
possible lube-related failures. The flow issue was soon
resolved: The E4OD turbine hubs that are used with bearings or
thrust washers all have lube passages for this reason (see
Figure 1).
The 4R100 has come by its flow problems
honestly. It has inherited them from the E4OD.
Figure 2 shows a typical 4R100 converter
with a multi-plate clutch. The converter-charge/clutch-release
oil passes between the stator support and the turbine shaft. At
the front stator bushing it must pass through the cavities that
direct the oil around the bushing. It then exits through the
three slots between the turbine shaft and the turbine hub. On
an E4OD converter there is an unrestricted flow between the
clutch and cover that not only keeps the clutch from dragging
but also continues on to the transmission lube circuit. This is
accomplished by the oil passing between the turbine hub and the
cover when there is no bearing and by passing through the
milled slots in the turbine hub when there is a bearing on the
hub.
The 4R100 turbine hub with the bearing has
no lube passages that bypass the bearing. The three slots on
the ID allow the oil to pass only between the turbine shaft and
the hub. Referring to Figure 2, you can see how the bearing
restricts the flow. Converter-charge/clutch-release oil must
either be forced through the bearing or squeezed between the
bearing and cover. For this reason, converter endplay is
critical in a 4R100. A minimum of 0.035 inch to 0.040 inch is
needed to allow sufficient clutch-release oil to keep the
clutch from dragging on the cover. You also must remember that
the greater the endplay, the more likely it is that you will
create an impact-related bearing failure. There is a fine line
between endplay clearance that is friendly to both the clutch
and the bearing and clearance that is not. Too much endplay
affects bearing life, and too little endplay affects clutch
life.
Some converter shops have made
modifications to improve flow. Milling slots across and below
the bearing-support surface like those on the E4OD shown in
Figure 1 is one way for the oil to bypass the bearing. Another
way is to mill slots in the cover (not shown) to accomplish the
same thing. Either of these methods will work, but you must
take care to ensure proper support for the bearing. You
don’t want to cause a bearing failure by improving the
flow. One enterprising shop even stole a page from the 5R110W
playbook. They drilled three diagonal holes in the 4R100
turbine hub to allow the oil to bypass the bearing (see Figure
3).
As with other lockup converters, the time
it takes to exhaust the oil from in front of the clutch for
lockup apply has an effect on clutch-apply feel. When the flow
of exhausting oil is restricted, the clutch apply is slower and
the feel will be softer. Clutch-apply oil enters the converter
through the rear stator cap, and a restriction at the cap also
can affect lockup feel. Normally, the in-and-out flow of oil is
metered very well in the non-lockup mode. The front
stator-support bushing meters the
converter-charge/clutch-release oil entering the converter, and
the rear stator cap meters the oil leaving the converter. With
proper end clearance they do a good job of balancing converter
charge. 
©2006 Transmission Digest